Hydrocarbon cracking process to produce olefins



Nov. 3, 1955 H. KREKELER ETAL 2,911,454

HYDROCARBON CRACKING PROCESS TO PRODUCE OLEFINS Filed May 3, 1954 def/ x94597016 Y Jack 6e 6/1: Jaw/909mm JA'I/C' nilml 41,4 1 vb if! INVENTORS- I ATTORNEYSI United States Patent HYDROCARBON CRACKING PROCESS TO PRODUCE OLEFINS Hans Krekeler, Konigstein, Taunus, and Wolfgang Kirschner, Giinther Relken, and Otto Waellnitz, Frankfurt am Main, Germany, assignors to Farbwerke Hoeclrst Aktiengesellschaft vormals Meister Lucius & Briining, Frankfurt am Main-Hoechst, Germany, a company of Germany Application May 3, 1954, Serial No. 427,254

Claims priority, application Germany May 7, 1953 8 Claims. (Cl. 260-683) This invention relates to a process conducted with circulating reaction masses in the hydrocarbon oil cracking.

In processes for cracking petroleum oils it is known to transfer the required heat to the oils by means of preheated and moved heat-carrying media. In some of the known processes the heat-carrying media are cycled by mechanical means, for instance bucket conveyers, or by pneumatic means such as air lifts, gas lifts, mass lifts, or the like. As lifting media there are used gases or vapors which are not formed during the process, in particular air, flue gas or steam. According to the transport method used, conveyance is carried out with or without application of pressure.

. For reasons of economy and to accord with the manufacturing conditions the mechanical conveyers have to operate at elevated temperatures. Consequently, the wear and tear, which is rather high even at ordinary tempera ture, is considerably increased, since high temperatures reduce the mechanical resistance and the resistance to wear, so that the commercial application of such plant is impossible in many cases. Moreover, the lifting capacity of such plant is not very high, being limited for structural reasons.

The use of pneumatic elevators with a compressed lifting medium (for instance 110 atmospheres gauge pressure in the case of mass lifts) requires the provision of shut-off devices at certain places in the system (for instance sluices with gate valves, bucket wheels or the like) which serve to maintain pressure tightness and which, owing to the working conditions, very soon get worn out. Operation troubles, high working costs and corresponding losses of output are the consequences. Pneumatic conveyers operated by air or flue gas involve the installation of expensive compressors or blowers. In many cases, however, a high pressure undesirably affects the course of the reaction and very often it must be avoided in view of its destructive effect on the construction material (reduction of mechanical resistance and corrosion-resistance at high temperatures).

The known pneumatic conveyers operating at low pressure (for instance 0.1-1 atmosphere gauge pressure) require the use of large quantities of pneumatic lifting media. Consequently, a great amount of energy is required for producing the necessary velocity of the gas and the pressure required; moreover, great heat losses and losses of reaction gases occur since the lifting gas, on being discharged and not recycled, cannot be prevented from carrying reaction gases with it.

Now, we have found a method of converting liquid bydrocarbons to normally gaseous partially unsaturated hydrocarbons which comprises circulating a granular heat carrying mass through a closed system including a reaction zone,.a reheating zone and an elevating conduit, heating said mass by indirect heat transfer in the reheating zone, applying the liquid hydrocarbon to the heated mass, passing the heated mass through the reaction zone at such a rate and temperatures between about 500 C.

and about 750 C. that the hydrocarbons are primarily converted to gases and minor quantities of liquid hydrocarbons and secondarily to a coke layer on the mass, recirculating the mass through the elevating conduit under the influence of an inert gaseous medium formed by the reaction.

This method is particularly advantageous as applied to processes for cracking hydrocarbon oils, such as petroleum. oil, fractions thereof, residual oils obtained in the working up of petroleum oil, bituminous tar oils or the like, the temperature being kept between about 500 C. and about 750 C. during all stages of the operation. It is very surprising that such reactions can be conducted in a cycle at these temperatures, with the production of valuable saturated and unsaturated hydrocarbons as well as valuable coke suitable, for instance, for the preparation of electrodes.

The application of the temperatures stated above is essential since at lower temperatures the composition of the final products would be changed detrimentally, in particular the unsaturated components which are of special value as intermediates, e.g. for the manufacture of plas tics, would not be formed.

The use of gases not evolved during the reaction, for instance air or steam, which are reacting with the hot coke, as lifting media in the reaction according to this invention would result either in a combustion of the valuable coke formed during the reaction or in an undesirable alteration of the reaction equilibrium.

Hence the combination of the process steps such as indirect heating of the heat carrier, especially of coke, to temperatures of between about 500 C. and about 750 C., and circulation of the gases formed by the reaction in a closed cycle, which combination is an object of the present invention, oliers unexpected advantages in the cracking of hydrocarbon oils.

As is usual with the gas lift, the conveyer medium is compressed to pressures which vary according to the kind of carrier used and which generally lie somewhat above atmospheric pressure up to half an atmosphere gauge pressure; it is then blown, through a nozzle arrangement or another suitable mixing device, into the elevating conduit together with the heat-carrying mass to be transported. After separation of the heat-carrying mass in a separating chamber (cyclone, filter or the like) the lifting medium is wholly or partially drawn in again by the compressor and reconducted to the nozzle or mixing device. In this manner the heat losses which are inevitable with the known processes (operating with gases like air and steam not formed by the cracking process and blowing off these gases) are essentially avoided; moreover, no additional device besides the above mentioned separating chamber is required for removing from the lifting gases the heat-carriers or solid or suspended matter formed during the reaction. When the reaction gases are used in whole or in part as the lifting medium in the process of cracking petroleum oils, for instance, the losses of reaction gas which are inevitable with the use of gaseous media not formed by the cracking process are reduced to a minimum without an additional purification system being required. Furthermore, the new process avoids the undesired influence on the course of the reaction often exerted by the formerly used gases not formed by the reaction which penetrated into and concentrated in the reaction vessel. In the new process, the course of reaction can be influenced, if desired, by current elimination of certain reaction products from the lifting gas. In addition, the undesired water gas reaction which takes place when steam is used as lifting medium at high temperatures cannot take place. Since, moreover, other lifting media can often be procured only at great expense, it is very economic to use the gases formed during the reaction as lifting medium. A further advantage resides in the fact that the reaction gas to be used in whole or in partywhen'the reaction is carried out under a slight excess pressure up to about /2 atmosphere gauge pressure, requires no additional lifting means .for removal from the-'reactionchamber. The gas is circulated at a speed ofabout lO-to about 50 m. per second. In the cracking Pf petroleum-oils it is possible to obtain in the .manner indicated (besides .the gaseous constituents) a coke which maybe'applied'with advantage to many commercial purposes. In certain circumstances, there may be added to thereaction gas used as lifting medium, inert gases not formed during the reaction and 'not reacting with the hot coke, e.g. nitrogen (or another inert gas), in an amountup to 50%.

An apparatus suitable for use for aprocess according 'to the invention is shown diagrammaticallyin the accompanying drawing and described below in a connection withthe process.

The process of the present invention, as applied to the cracking of petroleum oils, may be carried out as follows:

A granular heat-carrying mass, preferably round or oval-shaped bodies of, for instance, about 1 to about 20 mm. diameter, consisting of ceramic material, coke, petroleum coke or the like, is passed from separater 6 (see drawing) through heater 1 to reactor 2. The heat-carrier is heated to temperatures of about 500 C. to about 750 0., preferably 650 to 700 C., either directly, for instance. by directly blowing in combustion gases, or indirectly, for instance by means of a tube heater .la heated by a gas. It has been found that indirect heating of the heat carrier eg, of the petroleum coke obtained in cracking petroleum oil is essential and of particular advantage since, in this way, a partial combustion of the heat-carrying coke which would take place in direct heating is avoided. On its way to the reactor or, as it is especially shown in the drawing, in the upper part of the reactor the heat-carrying mass, in mixing zone 8, is contacted with the oil heated in a pre-heater, for instance to about 400 'C., and sprayed in, for instance, through a nozzle (the permissible preheating temperature depending on thenature of the reaction mixture used in each particular casepetroleum oil, oil residues or the like). By heat transfer the oil is evaporated and cracked in the reaction zone.

At outlet 9 the cracking gases are withdrawn fromthe reaction chamber and they are separated into the desired fractions in a rectifying or gas separating device 111, part of the reaction gas mixture or a fraction from the reac tion gases, especially saturated low hydrocarbons, e.g. ethane, propane, butane, being returned to the cycle at 13 and the remaining part being withdrawn at 12 for further use. Using said saturated low hydrocarbons as the lifting medium they are cracked in the tubular con- 'duitS owing to the contact with the hot coke, thus giving unsaturated hydrocarbons i.e. ethylene, propylene, butylene and the like. Between 6a and 13 the thus obtained unsaturated cracking gases may be separated from the cycling medium by a rectifying device (not shown). The petroleum coke formed, which entirelyor partially deposits on the heat carrier, is stripped off with steam blown in at 10 which is advantageously superheated. By this treatment the coke is freed from adhering heavy hydrocarbons (not shown in the drawing). Gases such as reaction gases or fractions therefrom or nitrogen, blown in at a suitable place or places, for instance at 10 and 11 into the reaction chamber 2, prevent the escaping of cracking gases into heater 1 or into discharge device 3.

The time of dwell of the heat carrier, for instance coke, in the reaction vessel is about 10 to about 60 minutes, preferably about 30 minutes. The gas formed during the reaction is removed from the reaction vessel within about 3 to about 30 seconds.

.The heatcarrier charged with coke is passed through a suitable discharge device 3 (air sluice, measure off device) to a nozzle arrangement 4 and from there the-carrierisblown by a gas current, produced by blower or fan 7, through tubularconduit 5 into. separator 6 (cyclone,

4 separating chamber, filter or the like). In separator 6 the heat carrier is separated from the gas current which, if desired, can be freed from powdered ingredients by an additional separating device 6a. The gas current then enters again blower 7.

At a suitable place in the pressure line of the fan, for instance at 14, the necessary quantities of additional gases can be introduced into :thecycle, if desired.

By an outlet in the separator 6 a part of the .heat carrier material can be removed from the cycle. Thedevice may be constructed so that, if desired, only heat carrying bodies of a certain maximum grain size remain in the cycle.

The rate of circulation of the heat carrier material-can be controlled for instance by a suitable construction of the measuring off device 3 which, if desired, can be replaced by a simple magnet vibrator or, in certain circumstances, can even be omitted, for instance if the quantity of the circulating lifting gas is regulated by altering the capacity of the fan 7.

The process of the present invention, for instance, allows of cracking petroleum oils with formation of hydrocarbons which besides saturated constituents (e,g. methane, ethane or like low hydrocarbons) substantially consist of unsaturated (olefinic) constituents; furthermore, a small proportion of unsaturated hydrocarbons with two double bonds, such as butadicne, is obtained in this way; the proportion of butadiene can be increased by introducing and recycling the butylene first obtained and again subjecting it to a cracking reaction in the tubular conduit 5.

The following example illustrates theinvention but it is not intended to limit it thereto:

Using an apparatus as described above and'illustrated in the drawing coke of a globular form and a size of about 5 to 15 mm. is circulated at a rate of 1.7 tons per hour and, at a temperature of 640 C. in the mixing-zone, 110 kilos of crude oil are injected perhour. Thereby, the temperature of the coke is decreased by about C.

After a time of dwell of about 30 minutes in the reactor, the coke is pneumatically elevated by the reaction gases and by means of indirect heating again brought to the initial temperature. The gaseous cracking products formed during the reaction leave the reactor after a time of dwell of 20 seconds whereas the coke formed deposits on the circulating coke. The crackingof the crude oil takes place endothermically.

The following quantities are obtained:

60.5 kilos=55% of gases containing 1 to 4 carbon-atoms and hydrogen, the said gases containing about 50% of olefines. The proportion of hydrogen contained in the 55% amounts to 0.4%. The saturated and unsaturated gaseous hydrocarbons contain more than 60% up to 80% of hydrocarbons which contain 2 to 4 carbon atoms.

38.5 kilos=35% of benzine (boiling below about 200 C.) and gas oil (boiling above about 200- C.).

11.0 kilos: 10% of coke.

'We claim:

1. A method for converting a liquid.hydrocarbon-- to normally gaseous, partially unsaturated hydrocarbons which comprises bringing the liquid hydrocarbon .into contact with a granular mass which consists substantially of particles having a diameter between about 1 and,20 mms. moving downwardly through a reaction-zoneata temperature between about 500 C. and about 750. C. for converting the liquid hydrocarbon primarily to gaseous hydrocarbons and secondarily to a coke layer .on the granular mass, removing the gaseous hydrocarbons separately from the reaction zone and circulating at leasta part thereof to a lifting zone, removing the granular mass from the reaction zone by a separate path'to:said lifting ,zone wherein said granular mass is lifted by said gaseous hydrocarbons to a separating zone above the reaction zone and a portion of the hydrocarbons is converted to unsaturated gaseous hydrocarbons, separating the normally gaseous, partially unsaturated hydrocarbons from the lifted granular mass, and reheating the granular mass by indirect heat transfer while moving said mass downwardly for recycling to the reaction zone.

2. A method as defined in claim 1 wherein the liquid hydrocarbon brought into contact with a granular mass is a member of the group consisting of petroleum oil, fraction of petroleum oil, residual oil obtained in working up petroleum oil and bituminous tar oil.

3. A method as defined in claim 1 wherein the gaseous hydrocarbons circulated to the lifting zone are members of the group consisting of ethane, propane and butane.

4. A method as defined in claim 1 wherein the lifting gas is recycled.

5. A method as defined in claim 1 wherein the lifting gas contains an additional inert gas in an amount up to 50% 6. A method as defined in claim 1 wherein a portion of the normally gaseous, partially unsaturated hydrocarbons separated from the lifted granular mass is withdrawn from the system, the balance being recycled to serve as lifting gas for further reaction with the granulated mass and enrichment with unsaturated hydrocarbons.

7. A method as defined in claim 1 wherein the reaction zone is under an absolute pressure of approximately one and one-half atmospheres and the mass inlet temperature is of the order of 500 C. to 750 C.

8. A method as defined in claim 1 wherein the reaction zone temperature is of the order of 650 C. to 700 C. and the yield of gases exceeds 50% of C C C -C hydrocarbons.

References Cited in the file of this patent UNITED STATES PATENTS 2,534,625 Robinson Dec..19, 1950 2,543,742 Evans Feb. 27, 1951 2,543,884 Weikart Mar. 6, 1951 2,661,324 Lefier Dec. 1, 1953 2,662,003 Waddill et a1 Dec. 8, 1953 2,694,038 Findlay Nov. 9, 1954 2,707,702 Watson May 3, 1955 2,731,400 Jahnig et al. Jan. 17, 1956 FOREIGN PATENTS Germany Feb. 14, 1952 

1. A METHOD FOR CONVERTING A LIQUID HYDROCARBON TO NORMALLY GASEOUS, PARTIALLY UNSATURATED HYDROCARBONS 